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Message-ID: <20221129095620.4c1a8056@gandalf.local.home>
Date: Tue, 29 Nov 2022 09:56:20 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: Andrew Yang <andrew.yang@...iatek.com>
Cc: Masami Hiramatsu <mhiramat@...nel.org>,
Matthias Brugger <matthias.bgg@...il.com>,
Casper Li <casper.li@...iatek.com>,
<linux-kernel@...r.kernel.org>,
<linux-arm-kernel@...ts.infradead.org>,
<linux-mediatek@...ts.infradead.org>
Subject: Re: [PATCH] mm/writeback: fix dereferencing NULL mapping->host
On Tue, 29 Nov 2022 11:32:59 +0800
Andrew Yang <andrew.yang@...iatek.com> wrote:
> From: "andrew.yang" <andrew.yang@...iatek.com>
>
> Check before dereferencing mapping->host
>
> Signed-off-by: andrew.yang <andrew.yang@...iatek.com>
> ---
> include/trace/events/writeback.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/trace/events/writeback.h b/include/trace/events/writeback.h
> index 86b2a82da546..56f6e114d3ed 100644
> --- a/include/trace/events/writeback.h
> +++ b/include/trace/events/writeback.h
> @@ -68,7 +68,7 @@ DECLARE_EVENT_CLASS(writeback_folio_template,
> strscpy_pad(__entry->name,
> bdi_dev_name(mapping ? inode_to_bdi(mapping->host) :
> NULL), 32);
> - __entry->ino = mapping ? mapping->host->i_ino : 0;
> + __entry->ino = mapping && mapping->host ? mapping->host->i_ino : 0;
I hate remembering precedence. Can we add parenthesis around this to be
clear?
__entry->ino = (mapping && mapping->host) ? mapping->host->i_ino : 0;
Thanks,
-- Steve
> __entry->index = folio->index;
> ),
>
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